The epidermal growth factor receptor (EGFR) is a member of the tyrosine kinase family of cell surface receptors that are widely expressed in epithelial, mesenchymal and neuronal tissues and play fundamental roles during development and differentiation. EGFR, also known as HER1 or c-erbB-1, is a 170 kDa transmembrane glycoprotein consisting of an extracellular ligand binding domain, a transmembrane region and an intracellular domain with tyrosine kinase activity (Ullrich et al., Human Epidermal Growth Factor cDNA Sequence and Aberrant Expression of the Amplified Gene in A-431 Epidermoid Carcinoma Cells, Nature, Vol. 309, 418-25 (1986)). Mammalian ligands that bind and activate EGFR include EGF, transforming growth factor α (TGFα), heparin-binding EGF-like growth factor, amphiregulin, betacellulin, epiregulin, and epigen (Singh, A. and Harris, R., 2005, Cellular Signaling 17:1183-1193). The binding of growth factors EGF or transforming growth factor α (TGFα) to the epidermal growth factor receptor results in receptor dimerization, auto-phosphorylation and induction of a tyrosine kinase cascade, leading ultimately to DNA synthesis and cell division.
EGFR is abnormally activated in many epithelial tumors, including those in non-small cell lung cancer, breast cancer, colorectal cancer, head and neck cancers, and prostate cancer (Adams, G. and Weiner, L., 2005, Nature Biotechnology, 23:1147-1157). Abnormal activation of EGFR can arise from overexpression of the receptor, gene amplification, activating mutations, overexpression of receptor ligands, and/or loss of regulators of EGFR activity (Baselga, J. and Arteaga, C., 2005, J. of Clin. Oncol. 23:2445-2459). Abnormally high EGFR activation results in phosphorylation of several intracellular substrates, which in turns gives rise to mitogenic signaling as well as other tumor-inducing activities. Consequently, EGFR is a target for anti-cancer therapeutic strategies which can potentially inhibit or reduce the receptor's aberrant expression.
Anti-cancer agents that target EGFR include monoclonal antibodies. The chimeric monoclonal antibody C225 (or cetuximab), which contains the murine variable region of mAb225 and a human IgG1 constant region, is presently available for treatment of irinotecan-refractory colon cancer in the United States and Europe (Baselga, J. and Arteaga, C., 2005, J. of Clin. Oncol. 23:2445-2459). In addition both human and humanized monoclonal antibodies to EGFR have been studied. The fully human antibody ABX-EGF (panitumumab) has an affinity for EGFR approximately 8-fold greater than that of C225 (Yang, X-D et al., 2001, Crit. Rev. Oncol./Hemat., 38:17-23). The affinity of humanized antibody EMD72000 (matuzumab) for EGFR is similar to that of C225 (Vanhoefer, U. et al., 2004, J. Clin Oncol., 22:175-184), and the affinity of humanized antibody h-R3 for EGFR is less than that of C225 (Crombet, T. et al., 2004, J. Clin. Oncol., 22:1646-1654). Complications have been observed in the clinic with doses of cetuximab higher than 100 mg/m2. They include skin toxicity that results in flushing, seborrheic dermatitis, and acneform rash (Herbst, R. and Langer, C., 2002, Semin. Oncol. 29:27-36).
There is a therapeutic need for an anti-EGFR antibody that binds EGFR with a high affinity and inhibits the abnormal activation of EGFR in epithelial tumors. A high affinity anti-EGFR antibody would allow lower doses to be administered to eliminate potential side effects such as skin toxicity. Moreover, there is a need to provide an anti-EGFR antibody that mitigates any potential immune response to the antibody that could be induced through multiple dosing. The present invention satisfies these needs and provides related advantages.